The structure of pretyrosine, a newly recognized amino-acid widely distributed among microorganisms and plants and shown to be a biosynthetic precursor of L-tyrosine and L-phenylalanine, will be characterized by the following methods: 1. chemical reactions in order to obtain different derivative structures of pretyrosine, and 2. spectroscopic techniques (lH-NMR, l3C-NMR, mass spect, IR, UV) of pretyrosine & its derivatives. Since prephenic acid represents a model structure, its spectroscopic properties will also be included. The stereochemistry of pretyrosine will also be established. The steric course of proton removal during the sequence between shikimate and chorismate will be investigated in a number of organisms known to possess the pretyrosine pathway.